The present invention relates to a pattern formation method for use in fabrication process for a semiconductor integrated circuit.
In accordance with the increased degree of integration of semiconductor integrated circuits and downsizing of semiconductor devices, there are increasing demands for further rapid development of lithography technique.
Currently, pattern formation is carried out through photolithography using exposing light of a mercury lamp, KrF excimer laser, ArF excimer laser or the like, and exposure systems are earnestly being developed in reducing the wavelength of exposing light and in increasing the NA (numerical aperture) of a demagnification projection lens.
In accordance with such development of the exposure systems, it is necessary to further improve the accuracy of the optical system, and a problem of unnecessary exposure caused by leakage light (flare) other than light necessary for the exposure has become more serious as a pattern to be formed is finer.
Now, a conventional pattern formation method will be described with reference to FIGS. 3A through 3D.
First, a chemically amplified resist material having the following composition is prepared:
Base polymer: poly((methoxymethyl acrylate) - (γ-butyrolactone  2 gmethacrylate)) (wherein methoxymethyl acrylate:γ-butyrolactonemethacrylate = 35 mol %:65 mol %)Acid generator: succinimide benzene sulfonate0.04 gSolvent: propylene glycol monomethyl ether acetate  20 g
Next, as shown in FIG. 3A, the chemically amplified resist material having the aforementioned composition is applied on a substrate 1, so as to form a resist film 2 with a thickness of 0.3 μm. Thereafter, as shown in FIG. 3B, the resist film 2 is subjected to pattern exposure by irradiating with ArF excimer laser 3 through a photomask 4.
Then, as shown in FIG. 3C, the substrate 1 is annealed with a hot plate at a temperature of 100° C. for 60 seconds. Thus, an exposed portion 2a of the resist film 2 becomes soluble in an alkaline developer because an acid is generated from the acid generator therein while an unexposed portion 2b of the resist film 2 remains to be insoluble in an alkaline developer because no acid is generated from the acid generator therein.
Subsequently, the resist film 2 is developed with a 2.38 wt % tetramethylammonium hydroxide developer (alkaline developer). Thus, a resist pattern 5 made of the unexposed portion 2b of the resist film 2 is obtained.
As shown in FIG. 3D, however, the resist pattern 5 is in a defective cross-sectional shape. When such a defective resist pattern 5 is used as a mask for etching a target film, the resultant pattern is also in a defective shape, which lowers the yield in the semiconductor fabrication process.